Pros
Microsoft believes its mission is to provide people around the world with tools that enable them to make their lives better. Tools that empower people to communicate, solve problems and innovate. Its a noble cause, for which one can feel some measure of pride. Microsoft is growing, perhaps not as much as we would all like, but it is increasing employees every year. The opportunities across professional disciplines, businesses and geographies are significant. Want to work overseas? Pick a country; transferring is relatively easy. Want to work on an incubation product, or perhaps the big dog Windows? Ok. Transferring between business groups can be done too. One can amass a diver portifolio of experiences here. It offers a unique career development landscape. And because Microsoft has such a diverse set of businesses, it can weather economic or geographic risk pretty well, meaning it is a place where one can feel some semblance of job security.
Cons
Microsoft is now a very large company. It has all the problems faced by other large compnaies: too much process, too many stakeholders to make decisions quickly, becoming political at the top, too disconnected from customers. It is a complex matrix that can often get in the way of doing the right thing, and doing it quickly.